Claude Sonnet 5 review after a week: it nearly matches Opus 4.8 on coding, beats it on Terminal-Bench, and runs at just $2/$10 — but the tokenizer bites.
Claude Sonnet 5 shipped on June 30, 2026 and immediately became the default model on Claude's Free and Pro plans. Anthropic's published numbers put it at 63.2% on SWE-bench Pro, a few points behind Opus 4.8's 69.2% but well ahead of Sonnet 4.6's 58.1%. On Terminal-Bench 2.1 it actually beats Opus 4.8 (80.4% vs 74.6%). Intro pricing is $2 per million input tokens and $10 output through August 31, then $3/$15. One detail is easy to miss: it ships with a new tokenizer that uses 1.0–1.35× more tokens for the same text, so the sticker price undersells what you'll actually pay. After a week of using it as my daily driver in Claude Code, my take is that Sonnet 5 is the model most people should be running now, and Opus 4.8 has shrunk to a specialist tool you reach for on the genuinely hard problems.
Anthropic ships models in three sizes: Haiku for cheap and fast, Sonnet for the middle, Opus for the frontier. Sonnet has always been the workhorse, the one that runs when you don't think about which model you're using. [Sonnet 5](https://www.anthropic.com/news/claude-sonnet-5) is the fifth generation of that workhorse, and the pitch is that the middle tier has crept close enough to the top tier that the top tier stops being the obvious choice.
It landed as the default for Free and Pro on claude.ai the day it launched, with access for Max, Team, and Enterprise, plus the API id `claude-sonnet-5` on the Claude Platform and inside Claude Code. That default placement counts for more than the benchmarks. Most Claude traffic never picks a model on purpose. Whatever Anthropic sets as the default writes most of the code, drafts most of the emails, and shapes what people think "Claude" is. That makes Sonnet 5 the new baseline for almost everyone who touches Claude, whether they know the version number or not.
I flipped my Claude Code default to it on launch morning and left it there for a week, running it against a Go service with a messy migration path, a Next.js dashboard, and a pile of one-off scripts. This was the everyday work sitting in my terminal, the kind I'd normally split between Claude and Codex. What stuck with me is that it finishes things. Multi-step tasks that used to stall halfway and wait for me to nudge them now run to completion on their own, and that single behavioral change is worth more than any single-digit benchmark bump.
Here are the numbers [Anthropic and early testers published](https://www.marktechpost.com/2026/06/30/anthropic-claude-sonnet-5-vs-sonnet-4-6-vs-opus-4-8-agentic-coding-benchmarks-api-pricing-and-cost-performance-tradeoffs-compared/), lined up against the two models Sonnet 5 is really being measured against: its own predecessor and the flagship one rung up.
| Benchmark | Sonnet 5 | Sonnet 4.6 | Opus 4.8 |
|-----------|----------|------------|----------|
| SWE-bench Pro (agentic coding) | 63.2% | 58.1% | 69.2% |
| Terminal-Bench 2.1 | 80.4% | — | 74